Steroidogenic cells require cholesterol as substrate for steroid hormone production. Cholesterol can be synthesized de novo from acetate or can enter the cell as a component of a serum lipoprotein. Under physiologic conditions, the majority of cellular cholesterol is supplied by lipoprotein. We propose to extend our observations on the relationship between serum lipoproteins and rat gonadal steroidogenesis under both in vitro and in vivo conditions. We plan to study the effects of pituitary hormones (FSH, LH, prolactin), steroids (estrogen, androgen) and growth factors (insulin, epidermal growth factor) on rat ovary granulosa cells and testis cells cultured in serum-free medium in the presence or absence of purified lipoproteins (human high and low density lipoprotein, rat high and low density lipoprotein). We will study the effects of lipoproteins on steroidogenesis during cellular differentiation and compare degradative and non-degradative mechanisms of cellular uptake of lipoprotein cholesterol. We will test the physiologic significance of the culture studies by utilizing in vivo techniques. In vivo infusion studies, using natural and synthetic lipoproteins, will examine the uptake and distribution of lipoprotein particle components within the various compartments of the ovary. The experiments outlined in this proposal will lead to a better understanding of the mechanisms which control gonadal steroidogenic function.